Field of the Invention
The present invention relates to a process for forming a multi-layer film useful as a resist under layer film to be used for fine processing in the manufacturing process of a semiconductor device, etc., and a patterning process using the multi-layer film formed by the process for forming a multi-layer film.
Description of the Related Art
In recent years, miniaturization of a pattern rule is in progress with a tendency of high integration and high-speed of LSI (Large-Scale Integrated circuit). While miniaturization of a pattern rule is progressing, in the lithography using a light exposure which has been currently used as a general technology, it is approaching the essential limit of resolution derived from a wavelength of a light source.
As a light source for lithography to be used for formation of a resist pattern, g-beam (436 nm) or i-beam (365 nm) of a mercury lamp, KrF excimer laser (248 nm), ArF excimer laser (193 nm), etc., has been widely used, and a double patterning has been investigated for further miniaturization.
The double patterning is a technology which is capable of doubling the resolution of the resist, and miniaturization of the device has been further accelerated thereby. Accompanying with the progress of miniaturization, a dry etching technology and a hard mask material each having high dimensional accuracy have been required. Also, needs for forming deep holes or grooves by dry etching has been heightened in manufacturing a three dimensional NAND memory or a capacitor of DRAM (Dynamic Random-Access Memory), etc. Under such a background, a hard mask excellent in etching resistance has been earnestly required.
On the other hand, to prevent from pattern collapse due to shrinkage of a size of the resist pattern, a thickness of the resist film has been made thin, and as a means to prevent from lowering in dry etching resistance due to thinning of the film, a multi-layer resist process has been used. The multi-layer process generally used in this case is a 3 layer (tri-layer) process in which a hydrocarbon film (hydrocarbon under layer film) is formed at a lower layer, an intermediate film (silicon-containing intermediate film) containing silicon is formed thereon, and a resist film is formed thereon. By providing antireflection effects to both of the silicon-containing intermediate film and the hydrocarbon under layer film, a highly antireflection effect can be obtained. In the age of a liquid immersion lithography in combination with a high NA (Numerical Aperture) lens, an incidence angle of light to the substrate becomes shallow so that reflection of the substrate is increased, and thus, an antireflection film having a high antireflection effect is required. Accordingly, a tri-layer process using a silicon-containing intermediate film and a hydrocarbon under layer film which are excellent in the antireflection effect was spread at one time.
However, in the multi-layer film for the tri-layer process in which a hydrocarbon series under layer film and an intermediate film containing silicon oxide have been formed by the spin coating, dry etching resistance for double patterning or digging deep holes or grooves is insufficient. On the other hand, a metal series film formed by sputtering or CVD (Chemical Vapor Deposition) is excellent in dry etching resistance as a hard mask, and in particular, a silicon film or a titanium nitride film has been widely used.
Also, for carrying out a lithography of a fine pattern with a narrow focus margin, it is necessary to make the base material flatten. However, a hard mask formed by sputtering or CVD cannot make unevenness of the base material flatten, so that it is necessary to make the film surface flatten by grinding with CMP (Chemical-Mechanical Polishing). On the other hand, a film formed by spin coating has a merit that the film surface of which can be made flatten by a simple and easy process only by spin coating and baking, by applying a material excellent in embedding characteristics.
Further, when the silicon-containing intermediate film is to be formed by sputtering or CVD, it is necessary to raise the temperature of the substrate to about 400° C. At this time, when a usual hydrocarbon film is applied as an under layer film, it is thermally decomposed so that a hydrocarbon material having high heat resistance at 400° C. is required for the under layer film. Such a material may be mentioned a novolac resin of fluorene bisnaphthol or an aldehyde condensate of carbazole and fluorenone (see Patent Documents 1 and 2).
In addition, in the tri-layer process, it has been proposed to form a negative pattern by developing it with an organic solvent. In this case, a margin for subjecting the silicon-containing intermediate film just below the resist to dry etching processing is insufficient since dry etching resistance of the resist film is markedly lowered due to the influences both of remaining the film in which the cyclic protective group having etching resistance has been deprotected, and decreasing the film thickness due to deprotection of the protective group. Thus, it has been investigated to make the silicon-containing intermediate film thin. At present, a film thickness of the silicon-containing intermediate film has been employed in the range of 30 to 40 nm. This has been determined by the reasons that reflection of the substrate becomes the minimum in this range, and the balance between the etching rate for transferring the pattern of the resist film and the etching rate for transferring the pattern of the silicon-containing intermediate film to the hydrocarbon film at the lower layer. On the other hand, to deal with insufficiency of dry etching resistance of the resist film as mentioned above, it is necessary to set the thickness of the silicon-containing intermediate film to 10 to 20 nm. However, when the silicon-containing intermediate film is made thin, two problems arise. One of which is that reflection of the substrate increases, whereby the margin of the lithography is reduced. Another of which is that sufficient resistance cannot be secured for processing the hydrocarbon film at the lower layer by dry etching using the pattern of the silicon-containing intermediate film as a mask.